<!DOCTYPE html>
<html class="writer-html5" lang="en" data-content_root="../">
<head>
  <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" />

  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>dead_code_scanner &mdash; The Logtalk Handbook v3.93.0-b01 documentation</title>
      <link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=d75fae25" />
      <link rel="stylesheet" type="text/css" href="../_static/css/theme.css?v=19f00094" />
      <link rel="stylesheet" type="text/css" href="../_static/css/custom.css?v=396eccfe" />

  
  <!--[if lt IE 9]>
    <script src="../_static/js/html5shiv.min.js"></script>
  <![endif]-->
  
        <script src="../_static/jquery.js?v=5d32c60e"></script>
        <script src="../_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script>
        <script src="../_static/documentation_options.js?v=c8100655"></script>
        <script src="../_static/doctools.js?v=9a2dae69"></script>
        <script src="../_static/sphinx_highlight.js?v=dc90522c"></script>
    <script src="../_static/js/theme.js"></script>
    <!-- begin favicon -->
    <link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png" />
    <link rel="icon" type="image/png" sizes="32x32" href="/favicon-32x32.png" />
    <link rel="icon" type="image/png" sizes="16x16" href="/favicon-16x16.png" />
    <link rel="manifest" href="/site.webmanifest" />
    <link rel="mask-icon" href="/safari-pinned-tab.svg" color="#5bbad5" />
    <meta name="msapplication-TileColor" content="#355b95" />
    <meta name="theme-color" content="#ffffff" />
    <!-- end favicon -->
    
    <link rel="index" title="Index" href="../genindex.html" />
    <link rel="search" title="Search" href="../search.html" />
    <link rel="next" title="debug_messages" href="debug_messages.html" />
    <link rel="prev" title="code_metrics" href="code_metrics.html" />
   
</head>

<body class="wy-body-for-nav"> 
  <div class="wy-grid-for-nav">
    <nav data-toggle="wy-nav-shift" class="wy-nav-side">
      <div class="wy-side-scroll">
        <div class="wy-side-nav-search" >

          
          
          <a href="../index.html" class="icon icon-home">
            The Logtalk Handbook
              <img src="../_static/logtalk.gif" class="logo" alt="Logo"/>
          </a>
              <div class="version">
                3.93.0
              </div>
<div role="search">
  <form id="rtd-search-form" class="wy-form" action="../search.html" method="get">
    <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" />
    <input type="hidden" name="check_keywords" value="yes" />
    <input type="hidden" name="area" value="default" />
  </form>
</div>
        </div><div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="Navigation menu">
    
              <p class="caption" role="heading"><span class="caption-text">Contents</span></p>
<ul class="current">
<li class="toctree-l1"><a class="reference internal" href="../userman/index.html">User Manual</a></li>
<li class="toctree-l1"><a class="reference internal" href="../refman/index.html">Reference Manual</a></li>
<li class="toctree-l1"><a class="reference internal" href="../tutorial/index.html">Tutorial</a></li>
<li class="toctree-l1"><a class="reference internal" href="../faq/index.html">FAQ</a></li>
<li class="toctree-l1 current"><a class="reference internal" href="index.html">Developer Tools</a><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="overview.html">Overview</a></li>
<li class="toctree-l2"><a class="reference internal" href="asdf.html"><code class="docutils literal notranslate"><span class="pre">asdf</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="assertions.html"><code class="docutils literal notranslate"><span class="pre">assertions</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="code_metrics.html"><code class="docutils literal notranslate"><span class="pre">code_metrics</span></code></a></li>
<li class="toctree-l2 current"><a class="current reference internal" href="#"><code class="docutils literal notranslate"><span class="pre">dead_code_scanner</span></code></a><ul>
<li class="toctree-l3"><a class="reference internal" href="#api-documentation">API documentation</a></li>
<li class="toctree-l3"><a class="reference internal" href="#loading">Loading</a></li>
<li class="toctree-l3"><a class="reference internal" href="#testing">Testing</a></li>
<li class="toctree-l3"><a class="reference internal" href="#usage">Usage</a></li>
<li class="toctree-l3"><a class="reference internal" href="#excluding-code-from-analysis">Excluding code from analysis</a></li>
<li class="toctree-l3"><a class="reference internal" href="#integration-with-the-make-tool">Integration with the <code class="docutils literal notranslate"><span class="pre">make</span></code> tool</a></li>
<li class="toctree-l3"><a class="reference internal" href="#caveats">Caveats</a></li>
<li class="toctree-l3"><a class="reference internal" href="#scanning-prolog-modules">Scanning Prolog modules</a></li>
<li class="toctree-l3"><a class="reference internal" href="#scanning-plain-prolog-files">Scanning plain Prolog files</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="debug_messages.html"><code class="docutils literal notranslate"><span class="pre">debug_messages</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="debugger.html"><code class="docutils literal notranslate"><span class="pre">debugger</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="diagrams.html"><code class="docutils literal notranslate"><span class="pre">diagrams</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="doclet.html"><code class="docutils literal notranslate"><span class="pre">doclet</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="help.html"><code class="docutils literal notranslate"><span class="pre">help</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="issue_creator.html"><code class="docutils literal notranslate"><span class="pre">issue_creator</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="lgtdoc.html"><code class="docutils literal notranslate"><span class="pre">lgtdoc</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="lgtunit.html"><code class="docutils literal notranslate"><span class="pre">lgtunit</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="linter.html"><code class="docutils literal notranslate"><span class="pre">linter</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="make.html"><code class="docutils literal notranslate"><span class="pre">make</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="packs.html"><code class="docutils literal notranslate"><span class="pre">packs</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="ports_profiler.html"><code class="docutils literal notranslate"><span class="pre">ports_profiler</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="profiler.html"><code class="docutils literal notranslate"><span class="pre">profiler</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="tutor.html"><code class="docutils literal notranslate"><span class="pre">tutor</span></code></a></li>
<li class="toctree-l2"><a class="reference internal" href="wrapper.html"><code class="docutils literal notranslate"><span class="pre">wrapper</span></code></a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../libraries/index.html">Libraries</a></li>
<li class="toctree-l1"><a class="reference internal" href="../ports/index.html">Ports</a></li>
<li class="toctree-l1"><a class="reference internal" href="../contributions/index.html">Contributions</a></li>
<li class="toctree-l1"><a class="reference internal" href="../glossary.html">Glossary</a></li>
<li class="toctree-l1"><a class="reference internal" href="../bibliography.html">Bibliography</a></li>
<li class="toctree-l1"><a class="reference internal" href="../genindex.html">Index</a></li>
</ul>

    <p class="caption"><span class="caption-text">External Contents</span></p>
    <ul>
    <li class="toctree-l1"><a class="reference internal" href="../../apis/index.html">APIs</a></li>
    <li class="toctree-l1"><a class="reference internal" href="https://logtalk.org">Logtalk website</a></li>
    <li class="toctree-l1"><a class="reference internal" href="https://github.com/LogtalkDotOrg/logtalk3">GitHub repo</a></li>
    </ul>
  
        </div>
      </div>
    </nav>

    <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap"><nav class="wy-nav-top" aria-label="Mobile navigation menu" >
          <i data-toggle="wy-nav-top" class="fa fa-bars"></i>
          <a href="../index.html">The Logtalk Handbook</a>
      </nav>

      <div class="wy-nav-content">
        <div class="rst-content">
          <div role="navigation" aria-label="Page navigation">
  <ul class="wy-breadcrumbs">
      <li><a href="../index.html" class="icon icon-home" aria-label="Home"></a></li>
          <li class="breadcrumb-item"><a href="index.html">Developer Tools</a></li>
      <li class="breadcrumb-item active"><code class="docutils literal notranslate"><span class="pre">dead_code_scanner</span></code></li>
      <li class="wy-breadcrumbs-aside">
              <a href="https://github.com/LogtalkDotOrg/logtalk3/blob/master/docs/handbook/sources/devtools/dead_code_scanner.rst" class="fa fa-github"> Edit on GitHub</a>
      </li>
  </ul>
  <hr/>
</div>
          <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
           <div itemprop="articleBody">
             
  <section id="dead-code-scanner">
<span id="library-dead-code-scanner"></span><h1><code class="docutils literal notranslate"><span class="pre">dead_code_scanner</span></code><a class="headerlink" href="#dead-code-scanner" title="Link to this heading"></a></h1>
<p>This tool detects <em>likely</em> dead code in Logtalk entities and in Prolog
modules compiled as objects. Predicates (and non-terminals) are
classified as dead code when:</p>
<ul class="simple">
<li><p>There is no scope directive for them, and they are not called,
directly or indirectly, by any predicate with a (local or inherited)
scope directive.</p></li>
<li><p>They are listed in <code class="docutils literal notranslate"><span class="pre">uses/2</span></code> and <code class="docutils literal notranslate"><span class="pre">use_module/2</span></code> directives but not
called.</p></li>
</ul>
<p>Besides dead code, this tool can also help detect other problems in the
code that often result in reporting false positives. For example, typos
in <code class="docutils literal notranslate"><span class="pre">alias/2</span></code> directives, missing scope directives, and missing
<code class="docutils literal notranslate"><span class="pre">meta_non_terminal/1</span></code> and <code class="docutils literal notranslate"><span class="pre">meta_predicate/1</span></code> directives.</p>
<p>Given the possibility of false positives, care must be taken before
deleting reported dead code to ensure that it’s, in fact, code that is
not used. A common cause of false positives is the use of conditional
compilation directives to provide implementations for predicates missing
in some systems or different predicate implementations per
operating-system.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">dead_code_scanner.lgt</span></code> source file implements the scanning
predicates for finding dead code in entities, libraries, and
directories. The source file <code class="docutils literal notranslate"><span class="pre">dead_code_scanner_messages.lgt</span></code> defines
the default translations for the messages printed when scanning for dead
code. These messages can be intercepted to customize the output, e.g.,
to make it less verbose or for integration with, e.g., GUI IDEs and
continuous integration servers.</p>
<section id="api-documentation">
<h2>API documentation<a class="headerlink" href="#api-documentation" title="Link to this heading"></a></h2>
<p>This tool API documentation is available at:</p>
<p><a class="reference external" href="../../apis/library_index.html#dead-code-scanner">../../apis/library_index.html#dead-code-scanner</a></p>
<p>For sample queries, please see the <code class="docutils literal notranslate"><span class="pre">SCRIPT.txt</span></code> file in the tool
directory.</p>
</section>
<section id="loading">
<h2>Loading<a class="headerlink" href="#loading" title="Link to this heading"></a></h2>
<p>This tool can be loaded using the query:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(dead_code_scanner(loader)).
</pre></div>
</div>
</section>
<section id="testing">
<h2>Testing<a class="headerlink" href="#testing" title="Link to this heading"></a></h2>
<p>To test this tool, load the <code class="docutils literal notranslate"><span class="pre">tester.lgt</span></code> file:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(dead_code_scanner(tester)).
</pre></div>
</div>
</section>
<section id="usage">
<h2>Usage<a class="headerlink" href="#usage" title="Link to this heading"></a></h2>
<p>This tool provides a set of predicates that allows scanning entities,
libraries, files, and directories. See the tool API documentation for
details. The source code to be analyzed should be loaded with the
<code class="docutils literal notranslate"><span class="pre">source_data</span></code> and <code class="docutils literal notranslate"><span class="pre">optimize</span></code> flags turned on (possibly set from a
loader file).</p>
<p>As an example, assume that we want to scan an application with a library
alias <code class="docutils literal notranslate"><span class="pre">my_app</span></code>. The following goals could be used:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">set_logtalk_flag</span>(source_data, on),
     <span class="k">set_logtalk_flag</span>(optimize, on).
yes

| <span class="o">?-</span> <span class="k">logtalk_load</span>(my_app(loader)).
...
yes

| <span class="o">?-</span> dead_code_scanner<span class="o">::</span>library(my_app).
...
</pre></div>
</div>
<p>For complex applications that make use of sub-libraries, there are also
<code class="docutils literal notranslate"><span class="pre">rlibrary/1-2</span></code> predicates that perform a recursive scan of a library
and all its sub-libraries. Conversely, we may be interested in scanning
a single entity:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> dead_code_scanner<span class="o">::</span>entity(some_object).
...
</pre></div>
</div>
<p>For other usage examples, see the <code class="docutils literal notranslate"><span class="pre">SCRIPT.txt</span></code> file in the tool
directory.</p>
</section>
<section id="excluding-code-from-analysis">
<h2>Excluding code from analysis<a class="headerlink" href="#excluding-code-from-analysis" title="Link to this heading"></a></h2>
<p>A set of options is available to specify code that should be excluded
when looking for unused predicates (and non-terminals):</p>
<ul>
<li><div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">exclude_directories(Directories)</span></code></div>
<div class="line">list of directories to exclude (default is <code class="docutils literal notranslate"><span class="pre">[]</span></code>); all
sub-directories of the excluded directories are also excluded;
directories may be listed by full or relative path</div>
</div>
</li>
<li><div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">exclude_files(Files)</span></code></div>
<div class="line">list of source files to exclude (default is <code class="docutils literal notranslate"><span class="pre">[]</span></code>); files may be
listed by full path or basename, with or without extension</div>
</div>
</li>
<li><div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">exclude_libraries(Libraries)</span></code></div>
<div class="line">list of libraries to exclude (default is
<code class="docutils literal notranslate"><span class="pre">[startup,</span> <span class="pre">scratch_directory]</span></code>)</div>
</div>
</li>
<li><div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">exclude_entities(Entities)</span></code></div>
<div class="line">list of entities to exclude (default is <code class="docutils literal notranslate"><span class="pre">[]</span></code>)</div>
</div>
</li>
</ul>
</section>
<section id="integration-with-the-make-tool">
<h2>Integration with the <code class="docutils literal notranslate"><span class="pre">make</span></code> tool<a class="headerlink" href="#integration-with-the-make-tool" title="Link to this heading"></a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">loader.lgt</span></code> file sets a make target action that will call the
<code class="docutils literal notranslate"><span class="pre">dead_code_scanner::all</span></code> goal whenever the <code class="docutils literal notranslate"><span class="pre">logtalk_make(check)</span></code>
goal (or its top-level abbreviation, <code class="docutils literal notranslate"><span class="pre">{?}</span></code>) is called.</p>
</section>
<section id="caveats">
<h2>Caveats<a class="headerlink" href="#caveats" title="Link to this heading"></a></h2>
<p>Use of local meta-calls with goal arguments only known at runtime can
result in false positives. When using library or user-defined
meta-predicates, compilation of the source files with the <code class="docutils literal notranslate"><span class="pre">optimize</span></code>
flag turned on may allow meta-calls to be resolved at compile-time and
thus allow calling information for the meta-arguments to be recorded,
avoiding false positives for predicates that are only meta-called.</p>
</section>
<section id="scanning-prolog-modules">
<h2>Scanning Prolog modules<a class="headerlink" href="#scanning-prolog-modules" title="Link to this heading"></a></h2>
<p>This tool can also be applied to Prolog modules that Logtalk is able to
compile as objects. For example, if the Prolog module file is named
<code class="docutils literal notranslate"><span class="pre">module.pl</span></code>, try:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(module, [source_data(on)]).
</pre></div>
</div>
<p>Due to the lack of standardization of module systems and the abundance
of proprietary extensions, this solution is not expected to work for all
cases.</p>
</section>
<section id="scanning-plain-prolog-files">
<h2>Scanning plain Prolog files<a class="headerlink" href="#scanning-plain-prolog-files" title="Link to this heading"></a></h2>
<p>This tool can also be applied to plain Prolog code. For example, if the
Prolog file is named <code class="docutils literal notranslate"><span class="pre">code.pl</span></code>, simply define an object including its
code:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span><span class="p">:- </span><span class="k">object</span>(code).
<span class="p">    :- </span><span class="k">include</span>(<span class="s">&#39;code.pl&#39;</span>).
<span class="p">:- </span><span class="k">end_object</span>.
</pre></div>
</div>
<p>Save the object to an e.g. <code class="docutils literal notranslate"><span class="pre">code.lgt</span></code> file in the same directory as
the Prolog file and then load it in debug mode:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(code, [source_data(on), optimize(on)]).
</pre></div>
</div>
<p>In alternative, use the <code class="docutils literal notranslate"><span class="pre">object_wrapper_hook</span></code> provided by the
<code class="docutils literal notranslate"><span class="pre">hook_objects</span></code> library:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(hook_objects(loader)).
...

| <span class="o">?-</span> <span class="k">logtalk_load</span>(code, [hook(object_wrapper_hook), source_data(on), optimize(on)]).
</pre></div>
</div>
<p>With either wrapping solution, pay special attention to any compilation
warnings that may signal issues that could prevent the plain Prolog from
being fully analyzed when wrapped by an object.</p>
</section>
</section>


           </div>
          </div>
          <footer><div class="rst-footer-buttons" role="navigation" aria-label="Footer">
        <a href="code_metrics.html" class="btn btn-neutral float-left" title="code_metrics" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left" aria-hidden="true"></span> Previous</a>
        <a href="debug_messages.html" class="btn btn-neutral float-right" title="debug_messages" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right" aria-hidden="true"></span></a>
    </div>

  <hr/>

  <div role="contentinfo">
    <p>&#169; Copyright 1998-2025, Paulo Moura.</p>
  </div>

  Built with <a href="https://www.sphinx-doc.org/">Sphinx</a> using a
    <a href="https://github.com/readthedocs/sphinx_rtd_theme">theme</a>
    provided by <a href="https://readthedocs.org">Read the Docs</a>.
   

</footer>
        </div>
      </div>
    </section>
  </div>
  <script>
      jQuery(function () {
          SphinxRtdTheme.Navigation.enable(true);
      });
  </script> 

</body>
</html>